Gordon Ramsay's Famous Chicken Sandwich (Crispy Baked) - My Home Made Recipe

Ingredients

• 500g cooked chicken meat (from 1 large roast chicken)
• 1 celery stem
• 1 green onion stem, finely sliced
• 75g walnuts, roughly chopped
• 3 tablespoons finely chopped cornichon or dill pickle
• 1 tablespoon finely chopped dill
• 160g whole egg mayonnaise
• 160g sour cream (or full-fat yogurt)
• 2 teaspoons Dijon mustard
• 1 tablespoon lemon juice (or white wine/cider vinegar)
• ½ teaspoon onion powder
• ¼ teaspoon garlic powder
• ¾ teaspoon cooking/kosher salt
• ¼ teaspoon black pepper
• 20 slices white sandwich bread (preferably day-old)
• Salted butter for spreading